1. Field of the Invention
The invention relates to a liquid crystal compound, and in particular to the synthesis and application thereof.
2. Description of the Related Art
Liquid crystal displays (hereinafter LCD) based on the twisted nematic (hereinafter TN) mode is the most common type of flat panel display (hereinafter FPD). The conventional TN LCD utilized in wristwatches or desk calculators can only contain a small number of matrix segments (e.g. 8*8), and therefore cannot be applied for displays with high information content, such as thin film transistor (TFT) LCDs, which actively switch a large number of segments (e.g. 1024*768). Nevertheless, despite performance improvements for TFT LCDs, conventional TN LCDs still hold advantages such as a lighter weight, smaller volume requirement, and lower power consumption. In the 1990s however, driven by developmental advancements for liquid crystal property, TFTs and the popularity of notebook computers, applications for TFT LCD usage have steadily increased. Coincidentally, during the later half of the 1990s, the popularity of fast switching helped to drive multimedia applications, thus allowing a cursor to follow fast movements of a mouse. With the visible area of a TFT LCD corresponding to that of a cathode ray tube (CRT), TFT LCDs were now being considered to be used as desktop monitors. However, increased application would be dependent upon improved viewing angle dependency of optical effect, especially contrast and color shift. As such, optical compensation films were introduced to improve optical effect. Meanwhile, also improving optical performance at the time was the development of new switching modes, such as in plane switching (IPS) and vertically aligned (VA) mode. Thus, allowing the TFT LCD computer monitors using the mentioned techniques to largely replace CRT monitors.
The prerequisite for liquid crystals is a broad nematic phase range of −40 to 100° C. in order to guarantee the so-called operating temperature range of LCDs. The clearing point of a liquid crystal is the temperature at which the liquid crystal phase vanishes. The clearing point must be at least 10° C. higher than the operating temperature of devices. In order to respond properly to an applied switching voltage, liquid crystals must exhibit dielectric anisotropy, defined as the difference of the dielectric constants parallel and perpendicular to the director of the nematic phase. Depending upon molecular structure, dielectric anisotropy can be positive (molecular dipole is parallel to the long axis of the molecule) or negative (molecular dipole is perpendicular to the long axis of the molecule). The switching time of an LCD, such as on-state to off-state or off-state to on-state, is proportional to the rotational viscosity (γ1) of the liquid crystal, such that Low γ1 may accelerate the switching time. The described properties are determined by the structural elements (side chain, rings, linking groups, and terminal group) of a liquid crystal molecule.
For achieving the above requirements, several papers such as J. Mater. Chem. 2004, 14, 1219 and patents such as U.S. Pat. Nos. 5,262,085, 6,143,198, or 6,685,995, disclose liquid crystal molecule designs. However, a novel liquid crystal molecule is still desired for improving LCD response time performance.